Wind



Ophelia wind speed analysis

The highest gust that occurred between 00 UTC on Monday and 07 UTC this morning from Ophelia was 96 mph at Roches Point on the south coast of Ireland, and occurred at 11 UTC (fig 1).

Figure 1

And just for completeness here are all the low-level stations that reported storm force gusts at anytime during that same period (fig 2).

Figure 2

On the face of it the warnings issued for the winds from ex-hurricane Ophelia look like they did there job, and that although three people died in Ireland, the warning saved many more, and that might well be true. But what about the accuracy of the warnings issued by both Met Eireann and the Met Office?

Met Eireann

If you remember Met Eireann amended their status Red and Amber warnings at around 9 am on Monday morning. They jumped the highest gusts expected from 80 mph to 93 mph, and extended the status Red to cover the entire country. If we look at the maximum gusts across Ireland in more detail (fig 3) you will see that the first warning they issued on Saturday for maximum gusts to 80 mph would have sufficed for all stations bar Roches Point, even across the north of Ireland all the gusts from the observing network were within the range of 50 to 80 mph stipulated in the original warning. The one thing that was wrong with Saturdays warning is that it didn’t single out the south coast as particularly vulnerable to the storm force southerly winds from Ophelia, especially the county of Cork which saw the highest gusts in excess of 90 mph. I’m not going to say whether the status red for the entire country was not warranted because I would likely put my foot right in it.

Figure 3

Met Office

Lets remind ourselves what the Met Office were warning us about as regards strong winds from Ophelia for the 16th in the UK.

Figure 4

Well as we’ve seen already the highest gust across Northern Ireland was 63 mph and did fall in the 55-65 mph range mentioned in the warning, but gusts in the range 65 to 75 mph or even 80 never occurred. And there lies the rub, because it’s never entirely clear from any warning issued by the Met Office what limits they use for yellow, amber or red warnings, and the reason why they don’t specify them is because it makes them impossible to verify. There is little doubt that the core of the strongest wind was along the south coast of Ireland, and up through the Irish Sea, in fact three stations in the northwest of Wales reported gusts of higher than 80 mph, and two of those, Aberdaron and Capel Curig reported gusts of 90 mph.

Figure 5

So using gusts of 70 mph or more as the basis for delineating the area of an amber warning, what should the area have looked like for the UK? Well on the basis of the wind speeds from the SYNOP stations it certainly wouldn’t have covered Northern Ireland, but instead stretched in an arc from Islay in the north down the Irish Sea possibly as far down as South Wales in the south (fig 6).

Figure 6

Looking back at the graphic from the NHC from Friday which shows the wind speed probabilities for Monday it shows look remarkably accurate. If the axis of the core of strongest winds had been aligned a little bit further east then it would have been spot on (fig 7). Perhaps we ought to leave it to the NHC to issue the warnings the next time a ex-hurricane heads our way.

Figure 7 – Courtesy of the NHC

The last post!

Figure 1

There’s still a number of stations reporting means of 50 knots or more (black triangles) across Wales, with gusts to 86 mph still occurring across the north of the country at 17 UTC (fig 1). It’s been quite a day, and I hope you’ve enjoyed these hourly reports on Ophelia’s progress. Apologies to those in Scotland where the winds are just starting to pick up, but I’m now packing it in for the day, I’ve been at it for nearly 12 hours! A full analysis on today’s gales and storm force winds from Ophelia tomorrow morning. I did manage to get to Tesco eventually so all in all a pretty good day.

Capel Curig hits 90 mph in gust

Figure 1

Gusts to 90 mph at Capel Curig in the last hour, and another at Aberdaron to 84 mph (fig 1). The table of mean wind speeds make interesting reading, quite a number of inland stations running a full gale especially across Northern Ireland, but Mumbles Head tops the lot, with a 64 mph storm force 11 mean wind speed at 16 UTC (fig 2), why can’t the BBC send a weather presenter there? I’ve seen a very poor selection of on-the-spot-reports across Ireland and western parts of the UK for today.

Figure 2

That’s torn it – a gust to 90 mph at Aberdaron

Figure 1

That’s torn it, there have been gusts higher than the 80 mph upper limit in the Met Office’s amber alert, but if we keep quiet and don’t mention it, they might just get away with it. The stations in question are Valley with a gust to 81 mph at 15 UTC, and Aberdaron with a gust of 90 mph, you just knew somehow that the upper limit of 80 mph was going to be exceeded, especially with a ferocious southwesterly 75 knot gradient (and I’m guessing here) running straight up the Irish Sea. I can’t see them upping their existing amber warning, although you never know.

Ophelia 14 UTC résumé

Figure 1

A quick résumé of the winds so far today from storm Ophelia (fig 1), the gust to 96 mph at Roches Point at 11 UTC remain the highest so far. It’s interesting to note, that apart from the winds from Roches Point, all the extremes gusts have remained below 80 mph. Winds are now peaking across the west and north of Wales at the moment (fig 2), so far they have been within the limits given in the amber warning.

Figure 2

Ophelia – 13 UTC

Figure 1

I reckon the very worst is now over for the south coast of Ireland, the wind has veered southwesterly and although it’s still gusting to more than 80 mph at Roches point the gradient should start to open a bit as the wind veers a little more into the west. Massive pressure rises over Valentia in the southwest now pushing Ophelia north-northeast where it should finally make landfall in county Clare or Galway. I see Weybourne in Norfolk reached 23.2°C at 13 UTC so it did break the warmest day record. By the way the contouring can’t handle Ophelia at all well but you probably already noticed that.

23.2°C at Manston equals the warmest 16th of October on record

Figure 1

There’s nothing quite like the British weather, with gusts of 67 mph on the Scilly Isles in the west on the 12 UTC chart (fig 1), and temperature of 23.2°C in the east at Manston, which more than likely makes it the warmest 16th October on record. In Ireland the storm force winds continue, and are still gusting in excess of 90 mph on the south coast, as Ophelia tracks slightly northwest of Valentia on the west coast, what about this for a pressure kick (fig 2).

Figure 2

Storm force 11 at Roches Point and gusting over 96 mph

Figure 1

It’s a good job Met Éireann wisely decided to up the status red this morning because the wind has been gusting to 96 mph at Roches Point on the south coast of Ireland (fig 1), and meaning 62 knots – that’s storm force 11 and just two knots of hurricane force 12 – at 11 UTC. Ophelia has still to make landfall, but must be very close to Valentia now, where the pressure at 11 UTC was 962.3 hPa and fell 9.6 hpa in the last hour.

Figure 2

Storm force 10 at Roches Point gusting 70 knots

Figure 1

There’s a storm force 10 south-southeasterly blowing at Roches Point with gusts to 70 knots on the 09 UTC chart (fig 1), Ophelia is still to the southwest of Valentia, where the pressure is falling like the proverbial clappers (fig 2).

Figure 2

Met Éireann up the status red warning for the entire country

Figure 1 – Courtesy of Met Éireann

I suspected that Met Éireann had limited the area of the status red warning that they had issued on Saturday. I just wondered how much they had been swayed by guidance from the UKMO, and underplayed Ophelia a little. Well they’ve remedied all that now by issuing a status red wind warning for the whole country, and increased the speed of the possible maximum gusts to 75 – 93 mph.